I met Meeko!
Based on info gathered from here and reddit, I took a guess that Meeko meets just after 9:00, 10:00 and/or 11:00 beside the stroller rentals.
Sure enough, he popped out around 9:05 today. Pocahontas was also out further up in the Oasis.
Neither appeared in the app, but it seems that they are anecdotally meeting regularly enough that there's a pattern.
Thanks all for your help!
He was also in Epcot a few days ago around 10 AM right inside International Gateway